Microdisplacement has no effect at all
Set the surface displacement to Displacement and Bump or to Dislplacement only (the default is bump, which will not deform the object, and only affect the shading, creating  &quot;fake&quot; relief.]1

Displacement needs vertices to operate on.
Here is a simple plane with 4 vertices and dislplacement. Here's the same plane subdivided 50 times: